The treatment of bone fractures in craniomaxillofacial regions generally proceeds by reducing the fractured bones to their anatomically correct positions, and thereafter fixing the bones in place. The bones may be fixed in place either by interosseous wiring, or by the technique of miniplate osteosynthesis. In either case, holes must be drilled in the bone structure for receiving the interosseous wire or screws for holding the miniplates to the bone.
In the drilling of holes into the bone structure, great care must be taken to ensure that the holes are drilled at precisely the correct place and to precisely the correct depth. If the holes are not drilled at the correct location, strain may be transmitted by screws to the surrounding bone structure. This may cause the bone to resorb in the vicinity of the screws, with the loosening of the hardware.
Similarly, complications, such as blindness, extraocular muscle dysfunction, retinal or corneal damage, and severe tissue trauma could result if the depth of holes is not gauged accurately. Accordingly, it is desirable during the drilling procedure to use an instrument which will prevent the surgeon from drilling too deeply into bones of craniomaxillofacial regions. Furthermore, it is also desirable to control the angle of the drilling to permit greater flexibility in the placement of implants. For example, if screws are to be placed into the frontal bone they are preferably inserted at a downward slanting angle with respect to the forehead. This ensures that neither the screws nor the drill bit enters the orbit. See M. Zide, "The Placement of Screws Above the Zygomaticofrontal Suture," 48 J. Oral & Maxillofacial Surg. 813-816 (1990).
A prior art drill guide, for controlling the angle and the depth of a hole drilled into anatomical bone, is disclosed in a catalog published in 1992 by Synthes Maxillofacial, a surgical supply company located in Paoli, Pa. This drill guide 1 is depicted in FIG. 1. The drill guide 1 has a threaded inner sleeve 2 which is screwed into a first opening 4a of an outer sleeve 4. By rotating the inner sleeve 2 with respect to the outer sleeve 4, the inner sleeve 2 may be extended from, or retracted into, the outer sleeve 4. A knurled nut 3 is provided which may be loosened to permit the rotation of the inner sleeve 2. After the inner sleeve 2 is adjusted to a desired length from the outer sleeve 4, the knurled nut 3 may be tightened to prevent rotation of the inner sleeve 2.
The outer sleeve 4 is attached to, and integral with, a handle 5. The outer sleeve 4 and handle 5 are connected so as to form an obtuse angle.
Such a drill guide 1 is useful in a variety of surgical operations. An exemplary surgical operation using the drill guide 1 proceeds as follows. An incision is made in the region of the fracture, the skin is retracted, and the bones are reduced to their correct anatomical positions. One or more threaded guide wires W are then inserted into the bones B, as depicted in FIG. 2, using a small diameter drill guide 1. The depth to which the guide wire W is inserted into the bones B is then measured by sliding a depth gauge sleeve 8 (FIG. 1) over the exposed portion of the guide wire W.
Knowing the depth of penetration of the guide wire W, the drill guide 1 may be adjusted so as to limit the drilling of a hole to a desired depth. A cannulated drill bit 6 (i.e., a drill bit with a central bore) is inserted into a second end 4b of the outer sleeve 4 until the quick coupling 7 of the drill abuts against the second end 4b of the outer sleeve 4 as depicted in FIG. 1. While the drill guide 1 is held in this position with one hand, the depth gauge sleeve 8 is inserted over the exposed portion of the drill bit 6a. Using the other hand, the knurled nut 3 is loosened, and the inner sleeve 2 rotated until the length of the exposed portion of the drill bit 6a equals the desired drilling depth. The knurled nut 3 is then tightened so that the inner sleeve 2 does not retract into, or extend from, the outer sleeve 4 during the drilling of the hole.
The adjusted drill guide 1 may then be inserted over the guide wire W until the inner sleeve 2 contacts the bone B, as depicted in FIG. 3. The cannulated drill bit 6 is inserted into the second end 4b of the outer sleeve 4 of the drill guide 1 over the guide wire W. The drill is then operated to drill into the bones B until the quick coupling 7 of the drill abuts against the second end 4b of the outer sleeve 4. Thus, the drill guide 1 acts as a stop, preventing the drilling of holes deeper than the length of the exposed portion of the drill bit 6a which protrudes from the drill guide 1 when the quick coupling 7 abuts against the second end 4b of the outer sleeve 4.
After the hole is drilled to the correct depth, a surgical screw is inserted into the hole and the guide wire is removed. The screws may secure an implant, such as a miniplate, to the bone structure. The miniplate holds the bone structure together so that it can heal.
Another special drill guide has been proposed for use in performing miniplate osteosynthesis in the orbital region. See, e.g., FIGS. 10.4-6, appearing on page 181 of Kruger et al, Oral and Maxillofacial Traumatology, Vol. 2, Quintessence Pub. Co., Inc., Chicago (1986). The special orbital drill guide consists of a handle, a curved C-shaped arm attached to the handle, and a plunging mechanism also attached to the handle. The plunging mechanism consists of an outer sleeve and inner sleeve, each of which has a through-going bore. The inner sleeve is slidably mounted within the outer sleeve, whereby it functions as a plunger. Both inner and outer sleeves are mounted on the handle in line with the C-shaped member.
To employ the special orbital drill guide, an assistant uses malleable retractors to retract the sides of the incision. With the surgeon holding the drill guide by the handle, the C-shaped arm is inserted into the incision and manipulated until it is positioned on and behind the orbital bone. The tip of the C-shaped arm is thus able to act as a protective stop behind the bone to be drilled. The outer sleeve is aligned with one of the holes in the miniplate and the inner sleeve is plunged forward through the outer sleeve until it comes in contact with a hole of a miniplate. Thereafter, a drill bit is inserted through the bore of the inner sleeve and a hole is drilled through the orbital bone in line with the hole of the miniplate. The tip of the C-shaped arm prevents the drill bit from penetrating too deeply into the ocular region.
The prior art drill guides, while useful, are not entirely satisfactory for their above-described procedures. The first prior art drill guide requires more than one hand to adjust the drilling depth, i.e., one hand to turn the knurled nut or inner sleeve and one hand to grasp the handle of the drill guide. Second, a separate depth gauge is required for adjusting the drilling depth of this drill guide.
The second prior art drill guide also has disadvantages. First, the special orbital drill guide, particularly its plunging mechanism, is difficult to manipulate and keep in place when drilling bones. Second, the C-shaped arm is not very well adapted to go around the orbital bone and act as a protective stop. The hemispherical shape of the arm extends too far into the orbit creating pressure on the eyeball which can cause contusion of extraocular muscles and retinal detachment. Third, the ocular drill guide may only be used in regions where the surgeon can position the C-shaped arm behind the bone to be drilled. Furthermore, the drill bit penetrates entirely through the bone to the other side. This is disadvantageous when it is desirable to drill less than entirely through the bone, such as when drilling near the far cortex.
Accordingly, it is an object of the present invention to provide a surgical instrument which will act as a drill guide for drilling anatomical bones and which can be adjusted with a single hand.
It is a further object of the present invention to provide a surgical drill guide which permits the drilling of a bore into anatomical bones at a controlled angle.
It is yet another object of the present invention to provide a drill guide which can limit the drilling of holes to depths less than or equal to the entire thickness of the bone.
It is yet a further object of the present invention to provide a drill guide which does not require access to opposite sides of the bones to be drilled.